Experimental Investigation of Free-Field and Shock-Initiated Implosion of Composite Structures

Abstract

The use of composites has attracted attention in underwater marine applications due to the array of advantages offered by these materials. Composite materials offer alternatives with reduced weight, improved corrosion resistance, and for submerged structures, greater potential operating depths. In addition, these materials provide improved stealth qualities by having very low thermal, acoustic, and magnetic signatures, increasing their appeal for military applications. For these reasons, the presence of composite materials in marine industries is increasing, and are currently used in several naval applications, such as sonar domes, masts, and hull sheathings. One of the biggest obstacles to widespread adaptation of composite materials is a lack of complete understanding and simple design rules for these materials, especially under extreme loading conditions. For this reason, the present work looks to expand the current knowledge of composite behavior by examining the problem of implosion. A comprehensive study on the hydrostatic implosion of carbon fiber reinforced epoxy composite tubes is conducted experimentally to examine the failure and damage mechanisms of collapse. Experiments are performed in a pressure vessel designed to provide constant hydrostatic pressure through the collapse. Filament-wound, braided, and roll-wrapped carbon-fiber/epoxy tubes are studied to explore the effect of geometry and reinforcement architecture on the modes of failure. 3-D Digital Image Correlation technique, which is first calibrated for the underwater environment, is used to capture the full-field deformation and velocities during the implosion event. Dynamic pressure transducers are employed to measure the pressure pulses generated by the event and evaluate its damage potential. The results show that composites with braided fabric reinforcements are found to have more damage potential to adjacent structures than those containing unidirectional reinforcements, as they release pressure waves with significantly greater impulse. The mechanisms and pressure fields associated with the hydrostatic implosion of glass-fiber reinforced polymer (GFRP) tubes with varying reinforcement are investigated using high-speed photography. Experiments are conducted in a large pressure vessel, designed to provide constant hydrostatic pressure throughout collapse. 3-D Digital Image Correlation (DIC) is used to capture full-field displacements, and dynamic pressure transducers measure the pressure pulse generated by the collapse. Results show that braided GFRP tubes release pressure waves with significantly greater impulse upon collapse as compared to filament-wound tubes, increasing their damage potential. An experimental study on the underwater buckling of composite and metallic tubes is conducted to evaluate and compare their collapse mechanics. Experiments are performed in a pressure vessel designed to